From: Bruno Marchal <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Sent: Sat, 27 Aug 2005 14:31:08 +0200
Subject: Re: subjective reality
>I do think so. See Deutsch book which make clear that the MWI is
based on comp. But it is explicit in Everett and in Wheeler
>assessment. From a strict logical point of view, ad hoc non comp
theory of MWI can be built but it is really out of topic.
> That may be Deutsch's opinion (though, again, I doubt he says
anything like that in his book) but I have read both
> Everett's thesis and both Wheeler's and DeWitt's defenses of it and
in no way shape or form does anything like YD
>even figure in them!!!
Literally, of course. YD is just a tools for explaining what it is "to
be like an Everett memory machine". It is implicit in reducing the
quantum uncertainty to the ignorance of which branch we are in a
superposition. Mathematically it can be justified by Gleason theorem or
by Graham Hartle type of infinite "frequency" operator. See the
Preskill's course on quantum computation which makes a nice summary.
I don't quite know what you mean by an "Everett memory machine"
neither could I find a definition (or a mention of it) in Preskill's
lectures. If by this you mean something like a machine whose memory
would track the successive branchings such
thing is innimical to the Everett notion that all information
contained in the universal wave function is relative and all
are conditional. Otherwise all "memory machines" are either (1)
classical and thus relativised to one branch or (2) quantal and
permanently standing in a superposition of branches so that their
memories would be as "un situated" as that of any other
subject. As for your "justification" I will just quote Preskill on a
piece of credo which is characteristic of Many-Worlders:
"My own view is that the Everett Interpretation of quantum theory
provides a satisfying explanation of measurement and
of the origin of randomness, but does not yet fully explain the
quantum mechanical rules for computing probabilities. A full
explanation should go beyond the frequency interpretation of
probability --- ideally it would place the Bayesian view of
probability on a secure objective foundation."
Though this is highly disputable in itself I think it shows quite well
where your statement above is mistaken.
> Let me understand this: your aim is to derive QM from an hypothesis
which, you know, is contradicted by QM ?!!!? Wow!
>I have already answered.
That is a Yes, than.
The current aim is to derive SWE (by which I mean the correct
geometrical-gravity extension of Schroedinger Wave Equation) from comp.
I don't expect to derive anything like SWE + collapse (although this is
not entirely excluded!).
What I have already proved is that
1) if you make the move from "SWE + collapse" to "SWE + comp", then
from purely arithmetical reasons you are forced to go the the quite
simpler theory "comp". This is the result of the UDA reasoning and you
are invited to criticize it: it presuppose some "folk-psychology" and
some passive understanding of Church thesis. See the slide of my 2004
SANE paper for a presentation is eight steps.
2) I translate that reasoning into the language of a large class of
universal machine and got more constructive description of the physics
you need (by "1)") to derive from comp. This is technically more
involved. It suppresses the need of the folk psychology.
I decrypt the above as a statement that you are NOT trying to derive
QM but a more general TOE, so that assuming YD is no
different than say, assuming subplankian determinism like 't Hooft or
Hiley do. I guess you need a lot more good luck than I first wished
Because you referred me to Deutsch's book I too a look at his own
defense of the Everett interpretation and was reminded also
of his not so passive understanding of the CT. As it turns out his
whole masterplan hinges on his belief that *CT is a result of
Physics* so he is really no great help to you.
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